As the demand for renewable energy grows, biomass material, that was once considered waste material, has become a key and valuable energy resource.
Biomass materials can be converted into biofuels, which is a form of bioenergy. There are two major routes for conversion of biomass materials to biofuels: biological conversion and thereto-chemical conversion. In the biological conversion process, fermentation of easily fermentable plant products to alcohols is achieved. These easily fermentable plant products can be extracted from corn kernels and sugar cane. One major disadvantage of this pathway is that only a fraction of the total carbon in the biomass material is converted to the final desired liquid hydrocarbon fuel.
In the thermo-chemical conversion process, solid biomass is converted to biofuels by the application of heat. One example of thermal conversion is pyrolysis, where the solid biomass material is decomposed by the action of heat into gaseous, liquids and solid decomposition products, essentially in the absence of air or oxygen. Historically, pyrolysis was a relatively slow process where the resulting liquid product was a viscous tar and non-reactive solids such as char and ash. However, researchers have discovered that a higher yield of a light pourable liquid was obtainable from biomass material through fast pyrolysis. Fast pyrolysis is a process in which biomass is rapidly heated to an elevated pyrolysis temperature for a very short time, and then rapidly cooled before chemical equilibrium can occur. In this way, the condensable vapors produced during fast pyrolysis are cooled to form the useful liquid product in the form of biofuel.
Biomass materials are typically composed of different structural and non-structural components, which have distinct chemical properties. The three main components in biomass materials are cellulose, hemicellulose and lignin, and all three have different optimal temperatures at which pyrolysis occurs. Cellulose, being the most stable component among the three, has the highest pyrolysis temperature. Typically, the fast pyrolysis process is optimized for cellulose pyrolysis because cellulose is the largest component of biomass material. This means that the fast pyrolysis is carried out at an elevated pyrolysis temperature, which is high enough to pyrolyse cellulose. One disadvantage at carrying out pyrolysis at such a high temperature is that the less stable lignin and hemicellulose tends to yield significant amounts of tar and gases instead of the condensable vapors that can be cooled to form biofuel. More disadvantageously, the tar and ash produced pollutes the biofuel that is produced, resulting in a biofuel that is of low calorific quality and which contains impurities.
There is a need to provide a method for producing biofuel from biomass material that overcomes, or at least ameliorates, one or more of the disadvantages described above.
There is also a need to provide a system for producing biofuel with a minimal amount of pollutants.